Braking devices for enabling vehicle speed control may be operated using vacuum. The vacuum may be provided by the engine via the engine intake manifold. Alternatively, a vacuum pump may be operated to provide the vacuum. As such, if there is insufficient vacuum to assist in the brake operation, a “hard pedal” condition may occur wherein the vehicle operator has to provide a larger brake pedal force than expected to attain the desired braking. Various approaches have been developed to mitigate such a “hard pedal” condition.
One such approach is shown by Kamiya et al. in U.S. Pat. No. 6,754,579. Therein, an engine controller automatically starts an engine upon determining that there is insufficient brake booster vacuum. In particular, Kamiya adjusts an automatic engine restart operation based on a brake pedal depression amount and a brake booster vacuum amount.
However, the inventors herein have recognized a potential issue with such an approach. As one example, the operator's hard pedal feeling may be prolonged while the engine is restarted and the appropriate amount of vacuum is generated. As another example, there may be conditions when even upon restarting the engine, the desired amount of vacuum cannot be generated due to other demands on the engine.
In one example, at least some of the above-mentioned issues may be at least partly addressed by a method of improving a brake pedal feel, comprising: adjusting a brake control variable in response to an impending change in a pedal feel, the impending change based on a hydraulic brake line pressure relative to a brake booster pressure. In this way, hydraulic brake line pressure may be increased before a hard pedal condition arises.
In one example, an engine controller may infer or identify the impending change in pedal feel based on a hydraulic brake pressure relative to the brake booster pressure (or vacuum level). In particular, in response to an impending change (e.g., increase) in the amount of pedal force required to displace the brake pedal, the controller may infer that a hard pedal condition may arise imminently. Accordingly, before the hard pedal condition occurs, the controller may increase the hydraulic brake line pressure by increasing an amount of hydraulic brake boost that is provided to the brake line. Specifically, an electrically-actuated hydraulic brake booster pump (e.g., an electric pump coupled to a hydraulic brake booster component or an ABS brake system component) may be operated and the pump output may be increased. Alternatively, or additionally, the vacuum level in the brake booster may be increased, for example, using vacuum from the engine intake manifold.
In this way, by increasing the hydraulic brake line pressure via adjustments to one or more brake system components before an impending hard pedal condition occurs, a hard pedal feel incurred by a vehicle operator during brake application can be averted. As such, this may improve the operator's driving experience.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.